/* ===== Variables ===== */
:root {
    --bg: #ffffff;
    --bg-secondary: #f7f7f8;
    --bg-card: #ffffff;
    --text: #1a1a1a;
    --text-secondary: #5a5a6a;
    --text-muted: #9a9aaa;
    --accent: #8b1a1a;
    --accent-hover: #6d1414;
    --border: #e5e5ea;
    --border-hover: #d0d0d8;
    --radius: 10px;
    --radius-sm: 6px;
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-serif: 'Source Serif 4', Georgia, serif;
    --shadow-sm: 0 1px 3px rgba(0,0,0,0.06);
    --shadow-md: 0 4px 16px rgba(0,0,0,0.08);
    --transition: 0.2s ease;
}

/* ===== Reset ===== */
*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
    font-family: var(--font-sans);
    background: var(--bg-secondary);
    color: var(--text);
    min-height: 100vh;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    display: flex;
    flex-direction: column;
}
a { color: inherit; text-decoration: none; }

/* ===== Nav ===== */
.nav-bar {
    max-width: 900px;
    margin: 0 auto;
    padding: 1.25rem 2rem;
}
.nav-link {
    display: inline-flex; align-items: center; gap: 6px;
    font-size: 0.82rem; font-weight: 500;
    color: var(--text-secondary);
    transition: color var(--transition);
}
.nav-link:hover { color: var(--text); }
.nav-link svg { transition: transform var(--transition); }
.nav-link:hover svg { transform: translateX(-3px); }

/* ===== Hero ===== */
.hero {
    text-align: center;
    padding: 1.5rem 2rem 2.5rem;
    max-width: 600px;
    margin: 0 auto;
}
.hero-title {
    font-family: var(--font-serif);
    font-size: 2.8rem;
    font-weight: 600;
    letter-spacing: -0.02em;
    color: var(--text);
}
.hero-subtitle {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin-top: 0.3rem;
}
.hero-link {
    color: var(--accent);
    text-decoration: underline;
    text-underline-offset: 2px;
    transition: color var(--transition);
}
.hero-link:hover { color: var(--accent-hover); }

/* ===== Papers Section ===== */
.papers-section {
    max-width: 900px;
    margin: 0 auto;
    padding: 0 2rem 4rem;
    flex: 1;
    width: 100%;
}
.papers-heading {
    font-size: 0.8rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.06em;
    font-weight: 600;
    margin-bottom: 1rem;
}

/* ===== Grid ===== */
.papers-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 1rem;
}

/* ===== Card ===== */
.paper-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.5rem;
    box-shadow: var(--shadow-sm);
    transition: box-shadow var(--transition), border-color var(--transition);
    display: flex; flex-direction: column;
    animation: fadeIn 0.35s ease both;
}
.paper-card:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--border-hover);
}
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(8px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Card Header */
.card-header {
    display: flex;
    align-items: flex-start;
    justify-content: space-between;
    gap: 0.75rem;
    margin-bottom: 0.75rem;
}

/* Tags */
.card-tags {
    display: flex; flex-wrap: wrap; gap: 0.35rem;
}

/* Updated Badge */
.card-updated {
    display: inline-flex;
    align-items: center;
    gap: 4px;
    font-size: 0.65rem;
    font-weight: 500;
    color: var(--text-muted);
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    padding: 0.2rem 0.55rem;
    border-radius: 100px;
    white-space: nowrap;
    flex-shrink: 0;
}
.card-tag {
    font-size: 0.65rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: var(--accent);
    background: rgba(139, 26, 26, 0.07);
    padding: 0.2rem 0.55rem;
    border-radius: 100px;
}

/* Title */
.card-title {
    font-family: var(--font-serif);
    font-size: 1.2rem;
    font-weight: 600;
    line-height: 1.35;
    color: var(--text);
    margin-bottom: 0.2rem;
}
.card-subtitle {
    font-size: 0.8rem;
    font-style: italic;
    color: var(--text-muted);
    margin-bottom: 0.6rem;
}

/* Meta */
.card-meta {
    display: flex; flex-wrap: wrap; gap: 0.4rem 1rem;
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-bottom: 0.6rem;
}
.card-meta span {
    display: flex; align-items: center; gap: 4px;
}
.card-meta svg {
    width: 13px; height: 13px;
    stroke: var(--text-muted);
}

/* Abstract */
.card-abstract {
    font-size: 0.85rem;
    color: var(--text-secondary);
    line-height: 1.6;
    flex: 1;
    margin-bottom: 1rem;
    display: -webkit-box;
    -webkit-line-clamp: 3;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

/* Actions */
.card-actions {
    display: flex; gap: 0.5rem;
    padding-top: 0.85rem;
    border-top: 1px solid var(--border);
}
.btn {
    display: inline-flex; align-items: center; gap: 5px;
    font-family: var(--font-sans);
    font-size: 0.78rem; font-weight: 600;
    padding: 0.45rem 0.9rem;
    border-radius: var(--radius-sm);
    cursor: pointer; border: none;
    transition: all var(--transition);
    text-decoration: none;
}
.btn-accent {
    background: var(--accent);
    color: #fff;
}
.btn-accent:hover {
    background: var(--accent-hover);
}
.btn-ghost {
    background: transparent;
    color: var(--text-secondary);
    border: 1px solid var(--border);
}
.btn-ghost:hover {
    color: var(--text);
    border-color: var(--border-hover);
    background: var(--bg-secondary);
}

/* ===== Empty ===== */
.empty-state {
    text-align: center;
    padding: 4rem 2rem;
    color: var(--text-muted);
}
.empty-icon {
    margin-bottom: 0.75rem;
    stroke: var(--text-muted);
}

/* ===== Footer ===== */
.site-footer {
    text-align: center;
    padding: 2rem;
    font-size: 0.78rem;
    color: var(--text-muted);
    border-top: 1px solid var(--border);
    background: var(--bg);
}
.site-footer a {
    color: var(--text-secondary);
    text-decoration: underline;
    text-underline-offset: 2px;
    transition: color var(--transition);
}
.site-footer a:hover { color: var(--text); }

/* ===== VIEWER PAGE ===== */

.viewer-body {
    display: flex; flex-direction: column;
    height: 100vh;
    overflow: hidden;
    background: var(--bg-secondary);
}
.viewer-toolbar {
    display: flex; align-items: center;
    gap: 1rem;
    padding: 0.65rem 1.25rem;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
    flex-shrink: 0;
}
.viewer-back {
    display: inline-flex; align-items: center; gap: 5px;
    font-size: 0.82rem; font-weight: 500;
    color: var(--text-secondary);
    transition: color var(--transition);
    white-space: nowrap;
}
.viewer-back:hover { color: var(--text); }
.viewer-back svg { transition: transform var(--transition); }
.viewer-back:hover svg { transform: translateX(-2px); }
.viewer-title {
    flex: 1;
    font-family: var(--font-sans);
    font-size: 0.82rem;
    font-weight: 600;
    color: var(--text);
    text-align: center;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}
.viewer-download {
    display: inline-flex; align-items: center; gap: 5px;
    font-size: 0.78rem; font-weight: 600;
    color: #fff;
    background: var(--accent);
    padding: 0.4rem 0.85rem;
    border-radius: var(--radius-sm);
    white-space: nowrap;
    transition: background var(--transition);
}
.viewer-download:hover { background: var(--accent-hover); }

.viewer-container {
    flex: 1;
    position: relative;
    background: #e8e8e8;
}
.viewer-frame {
    width: 100%; height: 100%;
    border: none;
}
.viewer-loading {
    position: absolute; inset: 0;
    display: flex; flex-direction: column;
    align-items: center; justify-content: center;
    gap: 0.75rem;
    color: var(--text-muted);
    font-size: 0.85rem;
}
.spinner {
    width: 28px; height: 28px;
    border: 3px solid var(--border);
    border-top-color: var(--accent);
    border-radius: 50%;
    animation: spin 0.7s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }
.viewer-fallback {
    position: absolute; inset: 0;
    display: flex; flex-direction: column;
    align-items: center; justify-content: center;
    gap: 1rem;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

/* ===== Responsive ===== */
@media (max-width: 640px) {
    .nav-bar, .papers-section { padding-left: 1rem; padding-right: 1rem; }
    .hero { padding: 1rem 1rem 2rem; }
    .hero-title { font-size: 2rem; }
    .paper-card { padding: 1.15rem; }
    .viewer-toolbar { padding: 0.5rem 0.75rem; }
    .viewer-title { font-size: 0.72rem; }
}